Projection optical system and projection-type image display apparatus

ABSTRACT

There is a need for providing a projection optical system that is appropriate for maintaining high resolution with low distortion, miniaturizing a reflector, decreasing the number of reflectors, and decreasing the depth and the bottom (or top) of a display used for a rear projection television, for example. The projection optical system according to the invention enlarges and projects images from a primary image surface existing at a reducing side to a secondary image surface existing at an enlarging side. The projection optical system has a first optical system L 11  and a second optical system L 12 . The first optical system L 11  forms an intermediate image (position II) of the primary image surface. The second optical system L 12  has a concave reflector AM 1  that forms the secondary image surface resulting from the intermediate image. A light beam travels from the center of the primary image surface and to the center of the secondary image surface and crosses an optical axis. The light beam is reflected on the concave reflector, crosses the optical axis again, and reaches the secondary image surface.

TECHNICAL FIELD

The present invention relates to a new projection optical system and anew projection-type image display apparatus. More specifically, theinvention relates to a technology that maintains high resolution withlow distortion, provides a small depth, and decreases the bottom (ortop) of a screen.

BACKGROUND ART

Recently, there is an increasing demand for rear projection televisions.The rear projection television has the feature of flat televisionrepresented by LCD (Liquid Crystal Display) direct-view television andPDP (Plasma Display Panel). Compared to these televisions, the rearprojection television provides a system that enlarges and projects animage display element as large as approximately one inch. Consequently,the rear projection television is available at low costs. The rearprojection television is relatively easily compliant with demands forhigh image quality of full HD (high definition) signal levelsrepresented by BS (Broadcasting Satellite) digital broadcasting andterrestrial digital broadcasting.

On the other hand, the rear projection television is mounted with alight source, an illumination optical system, and a projection opticalsystem. The rear projection television uses a large-diameter rear mirrorto project images onto a screen. FIG. 62 shows a well-known projectionmethod so that an optical axis a travels through the center of an imagedisplay element b and a screen c. According to such method, it isprincipally very difficult to decrease a depth d and a size e of thebottom of a display at the same time.

In addition, there is available an optical system that obliquelyprojects images onto the screen (hereafter referred to as obliqueprojection) so as to enlarge projected images and thin the rearprojection television (to decrease the depth).

For example, JP-A No. 100312/1993 proposes the projection optical systemthat uses a wide-angle lens having a large field angle. The projectionoptical system is provided with an image display element and a screenshifted from the projection optical system's optical axis and uses theend of the field angle for oblique projection.

As proposed in JP-A No. 80418/1993, the first projection optical systemintermediately forms image light based on a light bulb. The secondprojection optical system enlarges and projects the image on a screen.Optical axes of the respective projection optical systems areappropriately tilted for oblique projection. A recently proposedprojection optical system uses a reflector for oblique projection so asto prevent chromatic aberration from occurring in accordance withtendency toward wide angles.

The projection optical system shown in domestic re-publication of PCTinternational publication for patent applications WO01/006295 mainlyuses a refracting optical system g and an optical system composed of aconvex reflector f to implement oblique projection. FIG. 63 outlines theoptical system shown in domestic re-publication of PCT internationalpublication for patent applications WO01/006295.

JP-A No. 40326/2002 discloses the projection optical system having nochromatic aberration using four reflectors i (concave), j (convex), k(convex), and l (convex) arranged in order from an image display panel h(see FIG. 64).

The optical systems shown in these patent gazettes are rotationallysymmetric about the optical axis and perform oblique projection usingpart of the super-wide angle optical system.

JP-A No. 255462/2001 proposes the oblique projection optical systemusing an off-axial optical system. The projection optical system usesthe off-axial optical system to correct trapezoidal distortion. Inaddition, the projection optical system forms an intermediate imagebetween multiple reflectors m and reflector n to limit the reflectorsize (see FIG. 65).

As shown in domestic re-publication of PCT international publication forpatent applications WO01/006295, the projection optical system iscomposed of combination of the convex reflector f and the refractingoptical system g. Compared to a configuration using only the refractingoptical system, the proposed projection optical system facilitatesremoval of the chromatic aberration and enlargement of angles. On thecontrary, one reflector is used for most part of the divergence. Therefractive power needs to be decreased to some extent so as toappropriately correct the distortion and the image surface aberration.The projection optical system inevitably tends to enlarge the convexreflector f and increase the sag amount. This not only makes themanufacture of convex reflectors difficult, but also heightens a displaybottom portion (see reference symbol e in FIG. 62). In addition,applying this projection optical system to a rear projection televisionincreases the depth (see reference symbol d in FIG. 62).

The projection optical system shown in JP-A No. 40326/2002 has norefracting optical system and principally causes no chromaticaberration. Since no absorption occurs due to a lens, it is possible toprovide an optical system capable of high brightness. Since onlyreflectors are used to configure the system, however, the system tendsto be very susceptive to the surface accuracy and the assembly accuracyof each reflector and increase manufacturing costs. Since multiplereflectors i through l are vertically arranged, the bottom of thedisplay (see reference symbol e in FIG. 62) heightens. Increasing aprojection angle for a lower profile enlarges the reflectors, especiallythe last reflector l, making the manufacture of reflectors difficult.Applying this projection optical system to a rear projection televisionfurther enlarges the bottom of the display.

The projection optical system described in JP-A No. 255462/2001 uses anintermediate imaging surface and has an advantage of widening the angleand decreasing the reflector. On the contrary, the reflector isdecentered to cause decentering aberration. The remaining decenteredreflectors are used to correct the decentering aberration. At leastthree reflectors are needed. Applying this projection optical system toa rear projection television still leaves a difficulty in miniaturizingthe bottom of the display. Further, the reflectors are not rotationallysymmetric, but are configured to form a freely curved surface. Theprojection optical system tends to be very susceptive to the surfaceaccuracy and the assembly accuracy, make the manufacture difficult, andincrease manufacturing costs.

The present invention has been made in consideration of the foregoing.It is therefore an object of the present invention to provide aprojection optical system that is appropriate for maintaining highresolution with low distortion, miniaturizing a reflector, decreasingthe number of reflectors, and decreasing the depth and the bottom (ortop) of a display used for a rear projection television, for example.

DISCLOSURE OF THE INVENTION

To solve the above-mentioned problem, a projection optical systemaccording to the invention includes: a first optical system that formsan intermediate image of a primary image surface existing at a reducingside; and a second optical system having a concave reflector that formsa secondary image surface existing at an enlarging side according to theintermediate image. A light beam travels from the center of the primaryimage surface to the center of the secondary image surface, crosses anoptical axis of the first optical system, reflects on the concavereflector, crosses the optical axis again, and reaches the secondaryimage surface.

To solve the above-mentioned problem, a projection-type image displayapparatus according to the invention includes: a light source;modulation means for modulating and outputting light radiated from thelight source based on a video signal; and a projection optical systemfor enlarged projection from a primary image surface toward themodulation means to a secondary image surface toward a screen. Theprojection optical system includes: a first optical system that forms anintermediate image of the primary image surface; and a second opticalsystem having a concave reflector that forms the secondary image surfaceaccording to the intermediate image. A light beam travels from thecenter of the primary image surface to the center of the secondary imagesurface, crosses an optical axis of the first optical system, reflectson the concave reflector, crosses the optical axis again, and reachesthe secondary image surface.

According to the invention, the light beam travels from the center ofthe primary image surface to the center of the secondary image surfaceand crosses the optical axis of the first optical system. The light beamis then reflected on the concave reflector, crosses the optical axisagain, and reaches the secondary image surface. Following this lightpath, for example, the second optical system upward outputs light thatis formed on the secondary image surface from the approximatelyhorizontally disposed first optical system. The second optical systemonly needs to converge a slightly spreading light flux from a point onthe intermediate image for the first optical system onto a point on thesecondary image surface. Small optical parts can be used to realize thesecond optical system. Let us consider that the projection opticalsystem is used to construct a projection-type image display apparatus.In this case, for example, the second optical system may upward (ordownward) output light that is formed on the secondary image surfacefrom the approximately horizontally disposed first optical system. Inthis manner, it is possible to greatly decrease a space needed for theoptical system that is disposed at the bottom (or top) of the screen.

A projection optical system according to the invention is constructedfor enlarged projection from a primary image surface existing at areducing side to a secondary image surface existing at an enlarging sideand includes: a first optical system that forms an intermediate image ofthe primary image surface; and a second optical system having a concavereflector that forms the secondary image surface according to theintermediate image. A light beam travels from the center of the primaryimage surface to the center of the secondary image surface, crosses anoptical axis of the first optical system, reflects on the concavereflector, crosses the optical axis again, and reaches the secondaryimage surface.

A projection-type image display apparatus according to the inventionincludes: a light source; modulation means for modulating and outputtinglight radiated from the light source based on a video signal; and aprojection optical system for enlarged projection from a primary imagesurface toward the modulation means to a secondary image surface towarda screen. The projection optical system includes: a first optical systemthat forms an intermediate image of the primary image surface; and asecond optical system having a concave reflector that forms thesecondary image surface according to the intermediate image. A lightbeam travels from the center of the primary image surface to the centerof the secondary image surface, crosses an optical axis of the firstoptical system, reflects on the concave reflector, crosses the opticalaxis again, and reaches the secondary image surface.

In the projection optical system according to the invention, the lightbeam travels from the center of the primary image surface to the centerof the secondary image surface and crosses the optical axis of the firstoptical system. The light beam is then reflected on the concavereflector, crosses the optical axis again, and reaches the secondaryimage surface. Following this light path, the first optical system onceforms an intermediate imaging surface. The concave reflector is disposedafter the intermediate imaging surface to form an image on the secondaryimage surface again. There is no need for a large concave reflector. Itis possible to provide a large display that is appropriately correctedfor aberration and exhibits sufficient optical performance.

The projection-type image display apparatus according to the inventionuses the projection optical system to project an image formed by themodulation means onto the screen. Accordingly, the projection-type imagedisplay apparatus can not only have a low profile and miniaturize thebottom (or top) of the screen, but also display an enlarged image thatis appropriately corrected for aberration and exhibits sufficientoptical performance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1, as well as FIGS. 2 through 9, shows a first embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 2 is an enlarged view of the projection optical system.

FIG. 3 shows evaluation points on an image display element.

FIG. 4 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 3 onto a screen.

FIG. 5 shows distortion on the screen.

FIG. 6, as well as FIGS. 7 through 9, shows a configuration example of arear projection television together with part of light trajectories andprovides a perspective view, viewed from the rear of the screen.

FIG. 7 is a side view.

FIG. 8 is an enlarged perspective view showing the projection opticalsystem.

FIG. 9 shows an angle between the screen and an outmost light beam inlight flux directed to the screen from a mirror placed immediately infront of the screen.

FIG. 10, as well as FIGS. 11 through 18, shows a second embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 11 is an enlarged view of the projection optical system.

FIG. 12 shows evaluation points on an image display element.

FIG. 13 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 12 onto a screen.

FIG. 14 shows distortion on the screen.

FIG. 15, as well as FIGS. 16 through 18, shows a configuration exampleof a rear projection television together with part of light trajectoriesand provides a perspective view, viewed from the rear of the screen.

FIG. 16 is a side view.

FIG. 17 is an enlarged perspective view showing the projection opticalsystem.

FIG. 18 shows an angle between the screen and an outmost light beam inlight flux directed to the screen from a mirror placed immediately infront of the screen.

FIG. 19 shows correspondence between conditional equation (1) andassociated portions in the projection optical system according to thefirst embodiment.

FIG. 20, as well as FIGS. 21 through 27, shows a third embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 21 is an enlarged view of the projection optical system.

FIG. 22 shows evaluation points on an image display element.

FIG. 23 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 22 onto a screen.

FIG. 24 shows distortion on the screen.

FIG. 25, as well as FIGS. 26 through 27, shows a configuration exampleof a rear projection television together with part of light trajectoriesand provides a perspective view, viewed from the rear of the screen.

FIG. 26 is a side view.

FIG. 27 is an enlarged perspective view showing the projection opticalsystem.

FIG. 28, as well as FIGS. 29 through 35, shows a fourth embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 29 is an enlarged view of the projection optical system.

FIG. 30 shows evaluation points on an image display element.

FIG. 31 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 30 onto a screen.

FIG. 32 shows distortion on the screen.

FIG. 33, as well as FIGS. 34 and 35, shows a configuration example of arear projection television together with part of light trajectories andprovides a perspective view, viewed from the rear of the screen.

FIG. 34 is a side view.

FIG. 35 is an enlarged perspective view showing the projection opticalsystem.

FIG. 36, as well as FIGS. 37 through 40, shows a fifth embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 37 is an enlarged view of the projection optical system.

FIG. 38 shows evaluation points on an image display element.

FIG. 39 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 38 onto a screen.

FIG. 40 shows distortion on the screen.

FIG. 41, as well as FIGS. 42 through 45, shows a sixth embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 42 is an enlarged view of the projection optical system.

FIG. 43 shows evaluation points on an image display element.

FIG. 44 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 43 onto a screen.

FIG. 45 shows distortion on the screen.

FIG. 46, as well as FIGS. 47 through 50, shows a seventh embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 47 is an enlarged view of the projection optical system.

FIG. 48 shows evaluation points on an image display element.

FIG. 49 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 48 onto a screen.

FIG. 50 shows distortion on the screen.

FIG. 51, as well as FIGS. 52 through 55, shows an eighth embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 52 is an enlarged view of the projection optical system.

FIG. 53 shows evaluation points on an image display element.

FIG. 54 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 53 onto a screen.

FIG. 55 shows distortion on the screen.

FIG. 56, as well as FIGS. 57 through 60, show a ninth embodiment andoutlines a projection optical system used for a projection-type imagedisplay apparatus.

FIG. 57 is an enlarged view of the projection optical system.

FIG. 58 shows evaluation points on an image display element.

FIG. 59 is a spot diagram showing light radiated from the evaluationpoints shown in FIG. 58 onto a screen.

FIG. 60 shows distortion on the screen.

FIG. 61 shows correspondence between conditional equation (1) andassociated portions in the projection optical system according to thefourth embodiment.

FIG. 62 outlines the general configuration of a well-known rearprojection television.

FIG. 63 outlines the projection optical system shown in domesticre-publication of PCT international publication for patent applicationsWO01/006295.

FIG. 64 outlines the projection optical system shown in JP-A No.40326/2002.

FIG. 65 outlines the projection optical system shown in JP-A No.255462/2001.

FIG. 66 outlines the projection optical system shown in JP-A No.84576/2005.

BEST MODE FOR CARRYING OUT THE INVENTION

The following describes the best mode for carrying out the projectionoptical system and the projection-type image display apparatus accordingto the invention with reference to the accompanying drawings (see FIGS.19, 21, and 61 for the projection optical system and FIGS. 7 and 8 forthe projection-type image display apparatus).

The projection optical system according to the invention enlarges andprojects images from a primary image surface existing at a reducing sideto a secondary image surface existing at an enlarging side. Theprojection optical system has a first optical system and a secondoptical system. The first optical system has a concave reflector thatforms an intermediate image of the primary image surface. The secondoptical system forms the secondary image surface resulting from theintermediate image. A light beam travels from the center of the primaryimage surface to the center of the secondary image surface and crossesan optical axis. The light beam is reflected on the concave reflector,crosses the optical axis again, and reaches the secondary image surface.To summarize the image formation, the first optical system forms anintermediate image of the primary image surface. The concave reflectorthen converges the image to form a pupil that is formed as the secondaryimage surface. The first optical system generates an intermediate imageat a low magnification. The second optical system enlarges theintermediate image and forms it as the secondary image surface at aspecified magnification.

The optical system described in domestic re-publication of PCTinternational publication for patent applications WO01/006295 providesthe convex reflector with an effect of enlarging images. In this case,decreasing the convex reflector's curvature vignettes the light beam.The use of only one convex reflector cannot increase the enlargementfactor. Increasing the convex reflector's curvature makes the aberrationcorrection difficult and disables the sufficient optical performancefrom being obtained. To avoid this problem, multiple convex reflectorsmay be used to distribute the power and decrease the curvature of eachconvex reflector. However, a space large enough to dispose the multipleconvex reflectors further increases the optical system size.

When a concave reflector is used, by contrast, decreasing the curvaturehardly vignettes a light beam. The convex reflector or the concavereflector widens the field angle as follows depending on whether theyare positioned before or after the pupil.

(A) Between the pupil position and an image formation position(secondary image surface), the convex reflector widens the field angle.

(B) Between an image formation position (intermediate image) and thepupil position, the concave reflector widens the field angle.

Even when the concave reflector is used, however, there may be manyoptical surfaces between the pupil position and the secondary imagesurface. In such case, the optical surfaces must receive the light beamwidened by the concave reflector. These optical surfaces enlarge theoptical system. For this reason, the concave reflector needs to beplaced to the side of the secondary image surface. Accordingly, theprojection optical system according to the invention uses a firstoptical system to once generate an intermediate image. The concavereflector is subsequently placed to form the image as the secondaryimage surface. A concave reflecting mirror is appropriately positionedso as to form the pupil immediately after the concave reflector. In thismanner, the concave reflector is prevented from being enlarged.

In the projection optical system according to the invention, it ispreferable to construct the first and second optical systems whosesurfaces are rotationally symmetric about a common optical axis. Eachconstructive surface can be formed easily compared to a freely curvedsurface or an off-axial surface. It is possible to reduce manufacturingcosts and increase the surface accuracy of each constructive surface. Asa result, the excellent optical performance is easily available.

When only a single-sided concave reflector is used to construct thesecond optical system, it is possible to decrease the number ofcomponents and further save the space and costs. A concave or convexreflector can be placed before and after the concave reflector so as tofurther improve the aberration correction.

The first optical system is configured to form an intermediate imagetoward the primary image surface rather than toward the concavereflector of the second optical system. In this manner, it is possibleto prevent the concave reflector from being enlarged and form a largesecondary image surface that is appropriately corrected for aberrationand exhibits sufficient optical performance. When the first opticalsystem forms an intermediate image, particular attention needs to bepaid to a tendency to increase a distance between the primary imagesurface and the intermediate image. Increasing this distance alsoenlarges the optical system. It is necessary to decrease the distancebetween the first optical system and the intermediate image. As atarget, it is desirable to satisfy conditional equation (1) below:

Si/Ls<2  (1)

where Ls is the length of the first optical system, and Si is thedistance between the first optical system and the intermediate image.

When the left-hand side of the conditional equation (1) is greater thanor equal to 2, the distance between the primary image surface and thesecond optical system becomes long. The optical system remains largeeven when an intermediate plane mirror is used to shorten the distance.

The projection optical system according to the invention constructs apupil between the concave reflector and the secondary image surface toefficiently guide a light path. For this purpose, conditional equation(2) below must be satisfied:

S12>|R|/2  (2)

where |R|/2 is the focal distance of the concave surface, and S12 is thedistance between the last surface of the first optical system and theconcave reflector along the optical axis.

When the optical system has a reflector on the concave reflector'sprimary or secondary image surface, conditional equation (3) below mustbe satisfied:

SR12>|R|/2  (3)

where SR12 is the distance between the concave reflector and thepreceding or succeeding reflector along the optical axis.

When the projection optical system according to the invention isdisposed under a screen that forms the secondary image surface, a lightbeam close to the optical axis reaches the bottom of the screen and alight beam distant from the optical axis reaches the top thereof. Thatis, a light beam close to the optical axis causes a nearby imageformation position. A light beam distant from the optical axis causes afar image formation position. In order to form an image on the screenwithout curving the input signal, the system needs to be configured soas to decrease the concave reflector's paraxial curvature in accordancewith separation from the optical axis. That is, it is necessary toprovide a region satisfying conic constant K≦−1. It is especiallydesirable to be approximate to a paraboloidal surface (K=−1) or ahyperbolic curve (K<−1).

It is effective for the projection optical system according to theinvention to use a rotationally symmetric and aspheric surface. Inparticular, the image surface curvature can be freely controlled. Thismakes it possible to decrease the number of lenses and reduce an F value(the number of apertures). The low-cost and high-quality projectionoptical system can be realized.

The rotationally symmetric and aspheric shape is defined by equation 1as follows.

$\begin{matrix}{Z = {{( {h^{2}/r} )/\{ {1 + {\sqrt{\;}( {1 - {( {1 + K} ){h^{2}/r^{2}}}} )}} \}} + {A\; {4 \cdot h^{4}}} + {A\; {6 \cdot h^{6}}} + {A\; {8 \cdot h^{8}}} + \ldots}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

where

Z: Sag amount of the aspheric surface

h: Vertical height against the optical axis

r: Paraxial curvature radius

K: conic constant, and

Ai: Aspheric coefficient of degree i.

It may be effective for the projection optical system according to theinvention to use a rotationally symmetric and aspheric surfacecontaining an aspheric coefficient of odd-numbered degree. In this case,equation 2 below defines the shape of the rotationally symmetric andaspheric surface.

$\begin{matrix}{Z = {{( {h^{2}/r} )/\{ {1 + {\sqrt{\;}( {1 - {( {1 + K} ){h^{2}/r^{2}}}} )}} \}} + {A\; {1 \cdot h}} + {A\; {2 \cdot h^{2}}} + {A\; {3 \cdot h^{3}}} + {A\; {4 \cdot h^{4}}} + {A\; {5 \cdot h^{5}}} + {A\; {6 \cdot h^{6}}} + {A\; {7 \cdot h^{7}}} + {A\; {8 \cdot h^{8}}} + {A\; {9 \cdot h}} + \ldots}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

As shown in equation 2 above, the aberration of even-numbered degreeoccurs due to the term of odd-numbered degree, i.e., distance h from theoptical axis. When there is the term of h³, for example, thetwo-dimensional image surface curvature or distortion aberration occurs.When the concave reflector is provided with an appropriate asphericcoefficient, the distortion aberration can be more appropriatelycontrolled than using the aspheric surface according to equation 1above.

The projection-type image display apparatus according to the inventionincludes a light source, modulation means, and a projection opticalsystem. The modulation means modulates and outputs the light radiatedfrom the light source based on a video signal. The projection opticalsystem enlarges and projects images from the primary image surface atthe modulation means side to the secondary image surface at the screenside. The projection optical system includes first and second opticalsystems. The first optical system forms an intermediate image of theprimary image surface. The second optical system has a concave reflectorthat forms the secondary image surface composed of the intermediateimage. A light beam travels from the center of the primary image surfaceto the center of the secondary image surface, and crosses the opticalaxis of the first optical system. The light beam is further reflected onthe concave reflector, crosses the optical axis again, and reaches thesecondary image surface.

The projection-type image display apparatus according to the inventionuses the projection optical system according to the invention to projectan image formed by the modulation means on the screen. Theprojection-type image display apparatus according to the invention cannot only have a low profile and miniaturize the bottom (or top) of thescreen, but also display an enlarged image that is appropriatelycorrected for aberration and exhibits sufficient optical performance.

Let us consider using a transmissive screen. The screen is arranged atthe front of a cabinet. The cabinet includes the light source, themodulation means, and the projection optical system. The projectionoptical system enlarges and projects images onto the transmissive screenfrom the rear. In this manner, it is possible to construct a rearprojection television showing an external view similar to that of a flattelevision using a low-profile liquid crystal panel or PDP.

Further, let us suppose that the projection optical system is providedat the bottom of the cabinet. On the top of the cabinet, there may beprovided a plane mirror that reflects light output from the projectionoptical system and deflects the light so as to reach the transmissivescreen. In this manner, the projection-type image display apparatus canbe further slimmed.

When the second optical system forms a pupil for the intermediate imageonto the secondary image surface, the pupil may be formed outside alight flux traveling from the plane mirror to the transmissive screensurface. This increases the freedom of directing the light path in thecabinet. In addition, it is possible to provide a shielding unit havingan aperture at the pupil position where the light flux is most stoppeddown between the second optical system and the secondary image surface.This makes it easy to protect the projection optical system against dustand outside light.

The light beam travels from the center of the primary image surface tothe center of the secondary image surface and crosses the optical axiswithin a vertical plane. It may be preferable to provide reflectionmeans that reflects the light beam between the first and second opticalsystems and deflects the light beam within a horizontal plane. Provisionof the reflection means makes it possible to dispose the optical axis ofan optical member constructing the first optical system parallel to thescreen surface. The projection-type image display apparatus according tothe invention can be further miniaturized along the depth direction,i.e., can be further slimmed.

According to the projection-type image display apparatus described inJP-A No. 84576/2005 (see FIG. 66), plane mirror q is disposed so thatoutmost light p almost parallel reflects against screen o. In addition,projection optical system r is disposed opposite plane mirror q (e.g.,at the bottom when plane mirror q is positioned to the top). In thismanner, the depth is decreased (slimmed) and the bottom (or top) ofscreen o is reduced.

According to the projection-type image display apparatus described inJP-A No. 84576/2005, however, plane mirror q is disposed so that theoutmost light beam almost parallel reflects against screen o. Inaddition, projection optical system r is disposed opposite plane mirrorq. In this manner, the depth is slimmed and the bottom (or top) of thedisplay is reduced. When an attempt is made to further slim theprojection-type image display apparatus by keeping the bottom (or top)of the display small, it is necessary to slightly enlarge an angle ofoutmost light beam p against screen o. The projection optical system asshown in JP-A No. 84576/2005 uses many curved-surface reflectors andtherefore decreases the freedom of bending the light path. The depth ofthe projection optical system cannot be decreased. It is difficult tofurther slim the projection optical system.

The projection-type image display apparatus according to the inventionis provided with at least one plane reflector for directing the lightpath after reflected on the concave reflector. When the plane reflectoris positioned immediately before the screen, light beams are reflectedfrom the plane reflector to the screen. Of these light beams, theoutmost light beam passes through a position most distant from thescreen. Let us assume that the outmost light beam forms angle θ againstthe screen. The projection-type image display apparatus according to theinvention can be further slimmed by satisfying conditional equation (4)0.6>tan θ>0.05.

The following describes embodiments and numeric value examples of theprojection optical system and the projection-type image displayapparatus according to the invention in further detail with reference tothe accompanying drawings and tables.

First Embodiment

FIG. 1 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a first embodiment of the invention. FIG. 2 shows anenlarged view of the projection optical system.

In the diagram illustrating the first embodiment, P1 denotes an imagedisplay element as the modulation means. Based on a video signal, theimage display element P1 modulates the light emitted from a light source(not shown) to form the primary image surface. The image display elementP1 can represent a reflective or transmissive dot-matrix liquid crystalpanel, a digital micro mirror device (DMD), and the like. In thediagram, PP1 denotes a polarizing beam splitter (PBS), a 4P prism, a TIR(Total Internal Reflector) prism, and the like. STOP denotes adiaphragm. While the projector needs an illumination optical system toilluminate the image display element P1, the illumination optical systemis omitted from FIGS. 1, 2, and the other diagrams showing the firstembodiment.

L11 denotes a first optical system composed of a refracting opticalelement. L12 denotes a second optical system composed of a concavereflector AM1. The projection optical system is composed of the firstoptical system L11 and the second optical system L12 and guides thelight (primary image surface) image-modulated by the image displayelement P1 to the screen S1 to form an image (secondary image surface)on the screen S1. That is, the first optical system L11 forms anintermediate image at position II in FIG. 2. The image is then reflectedon a concave reflector AM1 of the second optical system L12 to form apupil image that is then formed on the screen S1. As shown in FIG. 2,the respective optical surfaces of the projection optical system arerotationally symmetric about an optical axis AXIS1. In FIG. 2, a brokenline indicates an unused and therefore removed part of the concavereflector AM1 of the second optical system L12.

Table 1 shows data for numeric value example 1 of applying specificnumeric values to the projection optical system according to the firstembodiment. In the following tables, surface numbers are provided inascending order like 1, 2, 3, and so on from the primary image surface(display device) to the secondary image surface (projected imagesurface). No surface number is given to the diaphragm. “INF” in thecurvature radius row indicates that the corresponding surface is flat.The refractive index and the Abbe number are applicable to the glassused for the primary image surface containing the flat surface and tothe e-line (546.1 nm). The inch size indicates the size of a diagonalline contained in the projected image surface. “E” represents thebase-10 exponential notation indicating an aspheric coefficient.

TABLE 1 Screen diagonal: 52.7 inches Numeric aperture at the displayelement side: 0.204 Glass (e-line refractive Surface number Curvatureradius Interval index/Abbe number) Display element INF 22.100 surface  1INF 12.000 1.83962/42.8  2 INF 27.300 1.51872/64.0  3 INF 6.050  481.82639 6.359 1.48914/70.2  5 −1254.73767 0.300  6 43.89754 11.8311.48914/70.2  7 −198.97423 0.200  8 43.61635 2.303 1.83930/37.1  925.81806 12.032 1.48914/70.2 10 −131.45439 1.656 11 −61.19711 1.9471.81184/33.0 12 30.63239 11.922 1.49845/81.2 13 −31.42185 0.200 14−32.45023 1.725 1.81184/33.0 15 36.45838 8.480 1.85505/23.6 16 −58.8400817.579 Diaphragm INF 47.218 17 43.97454 10.553 1.57125/55.8 18−1904.72192 12.159 19 Aspheric −1403.57952 7.000 1.49357/57.8 surface 20Aspheric 135.84325 0.300 surface 21 32.78514 12.508 1.58913/61.3 2244.75799 9.839 23 −56.04514 2.033 1.83930/37.1 24 43.91998 22.513 25−49.88309 9.344 1.49357/57.8 26 Aspheric −40.64674 320.000 surface 27Aspheric −85.89587 −439.276 Reflector surface Projected image INFsurface S19 K 2679.3838430 A4 −1.27105E−05 A6 1.10518E−08 A8−4.79662E−12 S20 K −65.0537440 A4 −1.04155E−05 A6 9.26604E−09 A8−5.80805E−12 S26 K −1.1618060 A4 −1.08919E−06 A6 −9.68945E−10 A86.42182E−13 S27 K −2.6454840 A4 −1.17532E−07 A6 6.31776E−12 A8−2.93186E−16 A10 8.80773E−21 A12 −1.55073E−25 A14 1.18177E−30

According to numeric value example 1, the image display element P1 hasan aspect ratio of 16:9, contains 1920×1080 pixels, and sizes to 0.61inches. The image display element P1 is enlarged to 52.7 inches forprojection. The numeric aperture toward an object is 0.204 (equivalentto F number 2.5). The pixel size is approximately 7 μm on the imagedisplay element P1 and approximately 0.608 mm on the screen S1.

FIG. 4 shows a spot diagram for the projection optical system accordingto numeric value example 1. FIG. 5 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element P1 shown in FIG.3. Reference wavelengths are 656.28 nm, 620.0 nm, 546.07 nm, 460.0 nm,and 435.84 nm and are given weights 2, 2, 3, 2, 1, respectively. Thescale for FIG. 4 is twice as large as one pixel on the screen S1. Asshown in FIG. 4, the sufficient image formation capability results. Asshown in FIG. 5, no remarkable image distortion is found and thesufficient capability results.

To dispose the projection optical system according to numeric valueexample 1 inside the cabinet CAB1 of the rear projection television, theprojection optical system needs to be compacted by folding the lightpath on plane mirrors MM11, MM12, and MM13 as shown in FIGS. 6 and 7.FIGS. 6 and 7 show constructions of elaborately folding the light pathby disposing the plane mirror MM13 between the projection optical systemand the screen S1 and the plane mirrors MM11 and MM12 between the firstoptical system L11 and the second optical system L12. The light beamtravels from the center of the primary image surface to the center ofthe secondary image surface and crosses the optical axis within avertical plane. In this case, the plane mirrors MM11 and MM12 reflectthe light beam between the first optical system and the concavereflector AM1 for the second optical system and deflect the light beamwithin a horizontal plane. When the projection optical system isdisposed at the bottom of the cabinet, for example, the plane mirrorMM13 is disposed at the top of the cabinet CAB1, reflects the lightoutput from the projection optical system, and deflects the light so asto reach the screen S1.

FIG. 7 is a side view. As shown in FIG. 9, the plane mirror MM13 is usedto fold the light path so that the outmost light beam forms angle θ ofapproximately 8.4 degrees against the screen. In this manner, theapparatus thickness can be 200 mm or less and the display bottom portioncan be small.

FIG. 8 partially enlarges the projection optical system in FIGS. 6 and7.

The projection-type image display apparatus according to the firstembodiment is compacted by folding the light path using the planemirrors MM11, MM12, and MM13. The invention is not limited to theabove-mentioned method of folding the light path. For example, it may bepreferable to dispose a plane mirror in the first optical system L11.Further, another plane mirror can be disposed between the plane mirrorMM13 and the concave reflector AM1.

The second optical system L12 forms a pupil AP1 (i.e., a portion wherethe light flux is converged) that forms an intermediate image for thefirst optical system L11 on the screen S1. The pupil AP1 is formedoutside the light flux from the plane mirror MM13 to the entire surfaceof the screen S1. When the projection optical system is disposed in thismanner, it is possible to provide a shielding box PB between a lightflux directed from the second optical system L12 to the plane mirrorMM13 and a light flux directed from the plane mirror MM13 to the entiresurface of the screen S1 so that the light flux directed to the screenS1 passes through an approximately minimum aperture TO1. The shieldingbox PB1 can protect the projection optical system (i.e., the firstoptical system L11 and the second optical system L12) against dustwithout blocking off the projected video light. Further, the shieldingbox PB1 blocks off outside light entering into the cabinet from thescreen S1. For example, the shielding box PB1 can prevent the outsidelight from being reflected on the concave reflector AM1 or the like ofthe second optical system L12 to become stray light and degrade thecontrast of the video projected on the screen S1.

Second Embodiment

FIG. 10 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a second embodiment of the invention. FIG. 11 showsan enlarged view of the projection optical system.

In the diagram illustrating the second embodiment, P2 denotes an imagedisplay element as the modulation means. Based on a video signal, theimage display element P2 modulates the light emitted from a light source(not shown) to form the primary image surface. The image display elementP2 can represent a reflective or transmissive dot-matrix liquid crystalpanel, a digital micro mirror device (DMD), and the like. In thediagram, PP2 denotes a polarizing beam splitter (PBS), a 4P prism, a TIR(Total Internal Reflector) prism, and the like. STOP denotes adiaphragm. While the projector needs an illumination optical system toilluminate the image display element P2, the illumination optical systemis omitted from FIGS. 10, 11, and the other diagrams showing the secondembodiment.

L21 denotes a first optical system composed of a refracting opticalelement. L22 denotes a second optical system composed of a concavereflector AM2. The projection optical system is composed of the firstoptical system L21 and the second optical system L22 and guides thelight (primary image surface) image-modulated by the image displayelement P2 to the screen S2 to form an image (secondary image surface)on the screen S2. That is, the first optical system L21 forms anintermediate image at position II in FIGS. 10 and 11. The image is thenreflected on a reflector AM2 of the second optical system L22 to form apupil image that is then formed on the screen S2. As shown in FIG. 11,the respective optical surfaces of the projection optical system arerotationally symmetric about an optical axis AXIS2. In FIG. 11, a brokenline indicates an unused and therefore removed part of the concavereflector AM2 of the second optical system L22.

Table 2 shows data for numeric value example 2 of applying specificnumeric values to the projection optical system according to the secondembodiment.

TABLE 2 Screen diagonal: 67.9 inches Numeric aperture at the displayelement side: 0.204 Glass (e-line refractive Surface number Curvatureradius Interval index/Abbe number) Display element INF 22.100 surface  1INF 12.000 1.83962/42.8  2 INF 27.300 1.51872/64.0  3 INF 6.050  448.02646 12.579 1.48914/70.2  5 −149.37820 0.300  6 470.90347 4.8691.48914/70.2  7 −141.59099 2.024  8 51.42610 8.429 1.49845/81.2  9−121.51292 1.377 10 −70.77524 2.158 1.81184/33.0 11 31.36886 12.9701.49845/81.2 12 −34.28097 0.200 13 −34.24547 1.872 1.81184/33.0 1439.69278 8.724 1.85505/23.6 15 −67.65941 22.810 Diaphragm INF 47.690 1641.92112 11.966 1.48914/70.2 17 −287.76955 7.924 18 Aspheric 1611.330877.000 1.49357/57.8 surface 19 Aspheric 118.54047 0.300 surface 2032.60197 14.000 1.48914/70.2 21 41.37986 10.096 22 −50.40323 2.0051.77621/49.4 23 44.94476 20.707 24 −52.51332 10.000 1.49357/57.8 25Aspheric −42.31242 325.000 surface 26 Aspheric −87.00193 −547.789Reflector surface Projected image INF 0.000 surface S18 K −51177.61327A4 −1.27130E−05 A6 9.95420E−09 A8 −3.65754E−12 S19 K −69.92292 A4−9.59429E−06 A6 7.57585E−09 A8 −3.71822E−12 S25 K −1.018512 A4−8.25367E−07 A6 −1.07783E−09 A8 5.13364E−13 S26 K −2.619353 A4−1.08108E−07 A6 5.56005E−12 A8 −2.48459E−16 A10 7.20728E−21 A12−1.22716E−25 A14 9.07427E−31

The image display element P2 has an aspect ratio of 16:9, contains1920×1080 pixels, and sizes to 0.61 inches. The image display element P2is enlarged to 67.9 inches for projection. The numeric aperture towardan object is 0.204 (equivalent to F number 2.5). The pixel size isapproximately 7 μm on the image display element P2 and approximately0.783 mm on the screen S2.

FIG. 13 shows a spot diagram according to numeric value example 2. FIG.14 shows distortion. Field angles (1) through (15) shown in the spotdiagram are respectively generated from positions (1) through (15) onthe image display element P2 shown in FIG. 12. Reference wavelengths are656.28 nm, 620.0 nm, 546.07 nm, 460.0 nm, and 435.84 nm and are givenweights 2, 2, 3, 2, 1, respectively. The scale for FIG. 13 is twice aslarge as one pixel on the screen S2. As shown in FIG. 13, the sufficientimage formation capability results. As shown in FIG. 14, no remarkableimage distortion is found and the sufficient capability results.

To dispose the projection optical system according to numeric valueexample 2 inside the cabinet CAB2 of the rear projection television, theprojection optical system needs to be compacted by folding the lightpath on plane mirrors MM21, MM22, and MM23 as shown in FIGS. 15 and 16.FIGS. 15 and 16 show constructions of elaborately folding the light pathby disposing the plane mirror MM23 between the projection optical systemand the screen S2 and the plane mirrors MM21 and MM22 between the firstoptical system L21 and the second optical system L22.

FIG. 16 is a side view. As shown in FIG. 18, the plane mirror MM23 isused to fold the light path so that the outmost light beam forms angle θof approximately 9.8 degrees against the screen. In this manner, theapparatus thickness can be 250 mm or less and the display bottom portioncan be small. Angle θ formed between the outmost light beam and thescreen preferably ranges between 2.9 and 31.0 degrees equivalent to tanθ ranging between 0.05 and 0.6.

FIG. 17 partially enlarges the projection optical system in FIGS. 15 and16.

The projection-type image display apparatus according to the secondembodiment is compacted by folding the light path using the planemirrors MM21, MM22, and MM23. The invention is not limited to theabove-mentioned method of folding the light path. For example, it may bepreferable to dispose a plane mirror in the first optical system L21.Further, another plane mirror can be disposed between the plane mirrorMM23 and the concave reflector AM2.

Obviously, the second embodiment can also use the shielding means asdescribed in the first embodiment. A pupil according to the secondoptical system L22 is positioned outside the outmost light beam of alight flux traveling from the plane mirror MM23 to the screen S2. Thereis no interference between the light flux traveling from the projectionoptical system to the plane mirror MM23 and the light flux travelingfrom the plane mirror MM23 to the screen S2. In addition, the light fluxis converged on the pupil.

Table 3 lists corresponding values for conditional equations (1) and (2)according to numeric value examples 1 and 2.

TABLE 3 Data associated with conditional equations Numeric value Numericvalue example 1 example 2 Remarks Si1 185 190 Distance between the lastsurface of the first optical system and intermediate image (1) in FIG. 3or 12 Si2 102 106 Distance between the last surface of the first opticalsystem and intermediate image (7) in FIG. 3 or 12 Si3 38 41 Distancebetween the last surface of the first optical system and intermediateimage (13) in FIG. 3 or 12 Ls 210 210 Total length of the first opticalsystem R −85.896 −87.002 Paraxial curvature of the concave reflector K−2.645 −2.619 Conic constant of the concave reflector Si1/Ls 0.88 0.90Si/Ls < 2 Si2/Ls 0.49 0.50 Si/Ls < 2 Si3/Ls 0.18 0.20 Si/Ls < 2 | R|/242.948 43.501 S12 > | R|/2 S12 320 325

Table 3 shows that both numeric value examples 1 and 2 satisfyconditional equations (1) and (2).

FIG. 19 shows intermediate image positions for the first optical systemL11 according to the above-mentioned embodiment 1. In FIG. 19, Si1, Si2,and Si3 denote distances between the first optical system L11 andintermediate image positions corresponding to the lowest, meddle, andhighest field angles on the screen, respectively. The positionscorrespond to points (1), (7), and (13) in FIG. 3. The distances areSi1≈185 mm, Si2≈102 mm, and Si3≈38 mm. Length Ls of the first opticalsystem L11 is 210 mm and satisfies conditional equation (1). Bothnumeric value examples 1 and 2 satisfy conditional equation (2) (seeTable 3).

Third Embodiment

FIG. 20 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a third embodiment of the invention. FIG. 21 showsan enlarged view of the projection optical system.

In the diagram illustrating the third embodiment, P3 denotes an imagedisplay element as the modulation means. Based on a video signal, theimage display element P2 modulates the light emitted from a light source(not shown) to form the primary image surface. The image display elementP3 can represent a reflective or transmissive dot-matrix liquid crystalpanel, a digital micro mirror device (DMD), and the like. In thediagram, PP3 denotes a polarizing beam splitter (PBS), a dichroic prism,a TIR (Total Internal Reflector) prism, and the like. STOP denotes adiaphragm. While the projector needs an illumination optical system toilluminate the image display element P3, the illumination optical systemis omitted from FIGS. 20, 21, and the other diagrams showing the secondembodiment.

L31 denotes a first optical system composed of a refracting opticalelement. L32 denotes a second optical system composed of reflectors R31and R32. In this case, R31 denotes a convex reflector toward the primaryimage surface and R32 denotes a concave reflector AM1 in the order of alight beam path from the image display element P3. The projectionoptical system is composed of the first optical system L31 and thesecond optical system L32 and guides the light (primary image surface)image-modulated by the image display element P3 to the screen S3 to forman image (secondary image surface) on the screen S3. That is, the firstoptical system L31 forms an intermediate image at position II in FIGS.20 and 21. The image is then reflected on reflectors R31 and R32 of thesecond optical system L32 to form a pupil image that is then formed onthe screen S3. As shown in FIG. 21, the respective optical surfaces ofthe projection optical system are rotationally symmetric about anoptical axis AXIS3. In FIG. 21, a broken line indicates an unused andtherefore removed part of the reflectors R31 and R32 of the secondoptical system L32.

Table 4 shows data for numeric value example 3 of applying specificnumeric values to the projection optical system according to the thirdembodiment.

TABLE 4 F number F/3.0 Inch size 73.1″ Glass (e-line refractiveCurvature radius Interval index/Abbe number) Display element INF 1.400surface 1 INF 20.700 2 INF 12.000 1.83962/42.8 3 INF 27.300 1.51872/64.04 INF 6.050 5 54.33486 12.294 1.49845/81.2 6 −89.63152 2.549 7 44.872699.194 1.49845/81.2 8 −106.88865 4.469 9 −49.15493 1.783 1.81184/33.0 1034.57615 2.987 11 39.16911 10.719 1.49845/81.2 12 −32.74038 2.658 13−33.88982 1.581 1.81184/33.0 14 −204.17705 7.015 15 −1450.76818 5.1461.85505/23.6 16 −47.28023 11.550 Diaphragm INF 26.546 17 −30.01628 1.8001.83962/42.8 18 −40.25509 27.966 19 46.38086 14.898 1.59142/61.0 20−231.41988 12.849 21 −91.96442 2.563 1.81263/25.3 22 −566.88378 0.300 2341.52448 10.030 1.67340/46.9 24 62.01431 9.000 25 −70.56814 6.8511.80831/46.3 26 46.59361 14.827 27 −54.43436 12.414 1.81081/40.5 28−47.66710 171.972 29 Aspheric surface 1.01174E−05 −149.000 Reflector(first mirror) 30 Aspheric surface 67.52094 485.861 Reflector (secondmirror) Projected image INF surface Aspheric coefficient for surface 29K −28531.19104 A4 −0.337498E−08 A6 0.665793E−11 A8 −0.831931E−15 A100.510008E−19 A12 −0.158764E−23 A14 0.200226E−28 Aspheric coefficient forsurface 30 K −2.694135 A4  0.170688E−06 A6 −0.116784E−10 A8 0.647442E−15A10 −0.199351E−19 A12  0.298396E−24 A14 −0.873758E−30

According to numeric value example 3, the image display element P3 hasan aspect ratio of 16:9, contains 1920×1080 pixels, and sizes to 0.61inches. The image display element P3 is enlarged to 73.1 inches forprojection. The F number is 3. The pixel size is approximately 7 μm onthe image display element P3 and approximately 0.845 mm on the screenS3.

FIG. 23 shows a spot diagram for the projection optical system accordingto numeric value example 3. FIG. 24 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element P3 shown in FIG.22. Reference wavelengths are 656.28 nm, 620.0 nm, 587.56 nm, 546.07 nm,460.0 nm, and 435.84 nm. The scale for FIG. 23 is twice as large as onepixel on the screen S3. As shown in FIG. 23, the sufficient imageformation capability results. As shown in FIG. 24, no remarkable imagedistortion is found and the sufficient capability results.

To dispose the projection optical system according to numeric valueexample 3 inside the cabinet of the rear projection television, theprojection optical system needs to be compacted by folding the lightpath on plane mirrors MM31 and MM32 as shown in FIGS. 25 and 26. FIGS.25 and 26 show constructions of elaborately folding the light path bydisposing the plane mirror MM32 between the projection optical systemand the screen S3 and the plane mirror MM31 between the first opticalsystem L31 and the second optical system L32. The light beam travelsfrom the center of the primary image surface to the center of thesecondary image surface and crosses the optical axis within a verticalplane. In this case, the plane mirror MM31 reflects the light beambetween the first optical system and the concave reflector for thesecond optical system and deflects the light beam within a horizontalplane. When the projection optical system is disposed at the bottom ofthe cabinet, for example, the plane mirror MM32 is disposed at the topof the cabinet, reflects the light output from the projection opticalsystem, and deflects the light so as to reach the screen S3.

FIG. 27 partially enlarges the projection optical system in FIGS. 25 and26.

The projection-type image display apparatus according to the thirdembodiment is compacted by folding the light path using the planemirrors MM31 and MM32. The invention is not limited to theabove-mentioned method of folding the light path. For example, it may bepreferable to dispose a plane mirror in the first optical system L31.Further, another plane mirror may be disposed between the plane mirrorMM32 and the concave reflector R32.

FIG. 26 is a side view. In this manner, the plane mirrors M31 and M32fold the light path. When the screen size is 73.1 inches with aspectratio of 16:9, apparatus thickness (depth) Dx defined for only theoptical system becomes smaller than or equal to 250 mm. When dimensionHx is assumed to be a height between the screen bottom and the lowestpart of the second optical system L32, Hx becomes smaller than or equalto 50 mm. The display bottom portion can be made small. Further, wefound the following as a result of examining the apparatus thickness andthe dimension of the display bottom portion with respect to variousscreen sizes. When the screen size ranges from 46 to 73 inches withaspect ratio of 16:9, the apparatus thickness defined for only theoptical system can become smaller than or equal to 250 mm. The heightbetween the screen bottom and the lowest part of the second opticalsystem L32 can be smaller than or equal to 50 mm. An actual apparatusmay include this optical system and may be provided with mechanicalparts such as a mirror and a cabinet. In such case, the apparatus canrealize actual outside dimensions including the thickness of 300 mm orless and the display bottom portion (the height between the screenbottom and the lowest part of the projection optical system) of 100 mmor less.

The second optical system L32 forms a pupil (i.e., a portion where thelight flux is converged) that forms an intermediate image for the firstoptical system L31 on the screen S3. The pupil is formed outside thelight flux from the plane mirror M32 to the entire plane of the screenS3. When the projection optical system is disposed in this manner, it ispossible to provide a shielding member (not shown, see FIG. 7) such as ashielding box between a light flux directed from the second opticalsystem L32 to the plane mirror M32 and a light flux directed from theplane mirror M32 to the entire surface of the screen S3. The shieldingmember is provided with an approximately minimum light transmissionaperture that allows the light flux directed to the screen S3 to passthrough. The shielding member can protect the projection optical system(i.e., the first optical system L31 and the second optical system L32)against dust without blocking off the projected video light. Further,the shielding member blocks off outside light entering into the cabinetfrom the screen S3. For example, the shielding member can prevent theoutside light from being reflected on the concave reflector or the likeof the second optical system to become stray light and degrade thecontrast of the video projected on the screen S3. The above-mentionedshield effect of the shielding member can be also applied to a fourthembodiment. A similar effect can be applied to projection-type imagedisplay apparatuses using projection optical systems according to thefifth to ninth embodiments.

Fourth Embodiment

FIG. 28 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a fourth embodiment of the invention. FIG. 29 showsan enlarged view of the projection optical system.

In the diagram illustrating the fourth embodiment, P4 denotes an imagedisplay element. A primary image surface is formed on the image displayelement P4. The image display element P4 can represent a digital micromirror device (DMD). STOP denotes a diaphragm. While the projector needsan illumination optical system to illuminate the image display elementP4, the illumination optical system is omitted from FIGS. 28, 29, andthe other diagrams showing the fourth embodiment.

L41 denotes a first optical system composed of a refracting opticalelement. L42 denotes a second optical system composed of reflectors R41and R42. The projection optical system is composed of the first opticalsystem L41 and the second optical system L42 and guides the light(primary image surface) image-modulated by the image display element P4to the screen S4 to form an image (secondary image surface) on thescreen S4. The first optical system L41 forms an intermediate image atposition II in FIGS. 28 and 29. The image is then reflected onreflectors R41 and R42 to form a pupil image that is then formed on thescreen S4. As shown in FIG. 29, the respective optical surfaces of theprojection optical system are rotationally symmetric about an opticalaxis AXIS4. In FIG. 29, a broken line indicates an unused and thereforeremoved part of the reflectors R41 and R42 of the second optical systemL42.

Table 5 shows data for numeric value example 4 of applying specificnumeric values to the projection optical system according to the fourthembodiment.

TABLE 5 F number F/3.0 Inch size 50″ Glass (e-line refractive Curvatureradius Interval index/Abbe number) Display element INF 54 surfaceDiaphragm INF 2.000 1 −52.65808 5.807 1.67000/47.97 2 −23.18766 0.937 3−20.50806 3.000 1.63003/35.48 4 −36.35509 0.100 5 60.64965 8.0531.49845/81.20 6 −33.07412 0.100 7 −58.53481 3.000 1.51978/51.85 841.88391 0.249 9 45.54872 3.341 1.76167/27.31 10 52.75286 0.576 1169.66878 8.817 1.49845/81.20 12 −32.45941 1.122 13 −26.48920 12.0001.52033/58.69 14 −87.21177 26.181 15 46.33716 14.214 1.62286/60.10 16−89.13615 0.500 17 −84.27186 8.911 1.67764/31.92 18 185.40020 4.858 19−81.21411 5.232 1.69416/30.92 20 58.72757 5.160 21 92.26113 13.9911.76167/27.31 22 −51.22638 0.100 23 −60.90220 3.000 1.52033/58.69 2447.28213 183.365 25 Aspheric surface 100.00000 −140.000 Reflector (firstmirror) 26 Aspheric surface 69.81598 368.158 Reflector (second mirror)Projected image INF surface Aspheric coefficient for surface 25 K−3.53735e+006 A4 −2.02633e−009 A6 1.58657e−012 A8 −8.56678e−017 A101.46304e−021 Aspheric coefficient for surface 26 K −2.34164e+000 A4 1.07990e−007 A6 −3.97824e−012 A8 1.26325e−016 A10 −1.14881e−021

A DMD is used as the image display element P4 that has an aspect ratioof 16:9, contains 1280×768 pixels, and sizes to 0.7 inches. The imagedisplay element P4 is enlarged to 50 inches for projection on the screenS4. The F number is 3. The pixel size is approximately 12 μm on theimage display element P4 and approximately 0.86 mm on the screen. Adiaphragm STOP is provided between the image display element P4 and theprojection optical system. ON light is reflected on the image displayelement P4, passes through the diaphragm STOP and the projection opticalsystem, and then reaches the screen S4. The diaphragm STOP interruptsOFF light. The ON light passes through the diaphragm STOP and enters therefracting optical system L41 to form an intermediate image at theposition II in FIGS. 28 and 10. The ON light is then reflected on thereflectors R41 and R42 to form a pupil image on the screen.

FIG. 31 shows a spot diagram for the projection optical system accordingto numeric value example 3. FIG. 32 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element P4 shown in FIG.30. Reference wavelengths are 656.28 nm, 620.0 nm, 587.56 nm, 546.07 nm,460.0 nm, and 435.84 nm. The scale for FIG. 31 is twice as large as onepixel on the screen. As shown in FIG. 31, the sufficient image formationcapability results. As shown in FIG. 32, no remarkable image distortionis found and the sufficient capability results.

To dispose the projection optical system according to numeric valueexample 4 inside the cabinet of the rear projection television, theprojection optical system needs to be compacted by folding the lightpath on plane mirrors M41 and M42 as shown in FIGS. 33 and 34. FIGS. 33and 34 show constructions of elaborately folding the light path bydisposing the plane mirror M42 between the projection optical system andthe screen S4 and the plane mirror M41 between the first optical systemL41 and the second optical system L42. FIG. 34 is a side view. Since theplane mirrors M41 and M42 are used to fold the light path in thismanner, the apparatus thickness can be 250 mm or less and the displaybottom portion can be small. FIG. 35 partially enlarges the projectionoptical system in FIGS. 33 and 34. The projection-type image displayapparatus according to the fourth embodiment is compacted by folding thelight path using the plane mirrors M41 and M42. The invention is notlimited to the above-mentioned method of folding the light path. Forexample, it may be preferable to dispose a plane mirror in the firstoptical system L41. Further, another plane mirror can be disposedbetween the plane mirror M42 and the concave reflector R42.

Fifth Embodiment

FIG. 36 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a fifth embodiment of the invention. FIG. 37 showsan enlarged view of the projection optical system.

In the diagram illustrating the fifth embodiment, P5 denotes an imagedisplay element. The image display element P5 forms the primary imagesurface. The image display element P5 can represent a reflectivedot-matrix liquid crystal panel, a digital micro mirror device (DMD),and the like. In the diagram, PP5 denotes a polarizing beam splitter(PBS), a dichroic prism, a TIR (Total Internal Reflector) prism, and thelike. STOP denotes a diaphragm. While the projector needs anillumination optical system to illuminate the image display element P5,the illumination optical system is omitted from FIGS. 36 and 37.

L51 denotes a first optical system composed of a refracting opticalelement. L52 denotes a second optical system composed of reflectors R51and R52. The projection optical system is composed of the first opticalsystem L51 and the second optical system L52 and guides the light(primary image surface) image-modulated by the image display element P5to the screen S5 to form an image (secondary image surface) on thescreen S5. The first optical system L51 forms an intermediate image atposition II in FIGS. 36 and 37. The image is then reflected onreflectors R51 and R52 to form a pupil image that is then formed on thescreen S5. As shown in FIG. 37, the respective optical surfaces of theprojection optical system are rotationally symmetric about an opticalaxis AXIS5. In FIG. 37, a broken line indicates an unused and thereforeremoved part of the reflectors R51 and R52 of the second optical systemL52.

Table 6 shows data for numeric value example 5 of applying specificnumeric values to the projection optical system according to the fifthembodiment.

TABLE 6 F number F/3.0 Inch size 55.8″ Glass (e-line refractiveCurvature radius Interval index/Abbe number) Display element INF 1.400surface 1 INF 20.700 2 INF 12.000 1.83962/42.8 3 INF 27.300 1.51872/64.04 INF 6.050 5 50.01335 12.300 1.49845/81.2 6 −102.48537 3.027 7 69.665888.000 1.49845/81.2 8 −102.39250 4.516 9 −49.22953 1.810 1.81184/33.0 1057.85879 1.068 11 36.59180 10.025 1.49845/81.2 12 −44.14826 5.030 13−35.10091 1.510 1.81184/33.0 14 −109.43158 10.879 15 125.64456 4.2591.85505/23.6 16 −92.16590 6.182 Diaphragm INF 17.304 17 −25.90402 1.8001.83962/42.8 18 −35.06784 43.616 19 Aspheric surface 59.62194 5.0001.51131/56.4 20 Aspheric surface 61.51696 1.000 21 51.89543 15.2001.59142/61.0 22 −573.87162 3.000 23 163.59945 5.117 1.81263/25.3 2472.87238 0.300 25 38.56059 13.000 1.67340/46.9 26 46.24911 13.439 27−77.70400 2.470 1.80831/46.3 28 50.57931 15.590 29 −62.19532 7.9551.81081/40.5 30 −49.34022 171.604 31 Aspheric surface 1.01174E−05−149.000 Reflector (first mirror) 32 Aspheric surface 72.72183 387.172Reflector (second mirror) Projected image INF surface Asphericcoefficient for surface 19 K −1.420362 A4 −0.131048E−04 A6 0.526113E−08A8 0.345041E−12 A10 0.611802E−16 Aspheric coefficient for surface 20 K−6.286742 A4 −0.104735E−04 A6 0.572168E−08 A8 −0.880556E−12 A100.356875E−15 Aspheric coefficient for surface 31 K −28531.19104 A4−0.523359E−07 A6 0.157209E−10 A8 −0.172128E−14 A10 0.101543E−18 A12−0.309504E−23 A14 0.381546E−28 Aspheric coefficient for surface 32 K−2.417695 A4  0.116220E−06 A6 −0.588887E−11 A8 0.248721E−15 A10−0.212607E−20 A12 −0.170341E−24 A14  0.475557E−29

According to numeric value example 5, the image display element P5 hasan aspect ratio of 16:9, contains 1920×1080 pixels, and sizes to 0.61inches. The image display element P5 is enlarged to 55.8 inches forprojection. The F number is 3.0. The pixel size is approximately 7 μm onthe image display element P5 and approximately 0.64 mm on the screen S5.

FIG. 39 shows a spot diagram for the projection optical system accordingto numeric value example 5. FIG. 40 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element P5 shown in FIG.38. Reference wavelengths are 656.28 nm, 620.0 nm, 587.56 nm, 546.07 nm,460.0 nm, and 435.84 nm. The scale for FIG. 39 is twice as large as onepixel on the screen S5. As shown in FIG. 39, the sufficient imageformation capability results. As shown in FIG. 40, no remarkable imagedistortion is found and the sufficient capability results.

When the projection optical system according to the fifth embodiment isapplied to a projector (projection-type image display apparatus), theprojection optical system can be slimed by disposing plane mirrors atappropriate positions similarly to the above-mentioned first and fourthembodiments.

Sixth Embodiment

FIG. 41 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a sixth embodiment of the invention. FIG. 42 showsan enlarged view of the projection optical system.

In the diagram illustrating the sixth embodiment, P6 denotes an imagedisplay element. The image display element P6 forms the primary imagesurface. The image display element P6 can represent a reflectivedot-matrix liquid crystal panel, a digital micro mirror device (DMD),and the like. In the diagram, PP6 denotes a polarizing beam splitter(PBS), a dichroic prism, a TIR (Total Internal Reflector) prism, and thelike. STOP denotes a diaphragm. While the projector needs anillumination optical system to illuminate the image display element P6,the illumination optical system is omitted from FIGS. 41 and 42.

L61 denotes a first optical system composed of a refracting opticalelement. L62 denotes a second optical system composed of reflectors RR61and RR62. The projection optical system is composed of the first opticalsystem L61 and the second optical system L62 and guides the light(primary image surface) image-modulated by the image display element P6to the screen S6 to form an image (secondary image surface) on thescreen S6. The first optical system L61 forms an intermediate image atposition II in FIGS. 41 and 42. The image is then reflected onreflectors RR61 and RR62 to form a pupil image that is then formed onthe screen S6. In this case, RR61 denotes a concave reflector and RR62denotes a convex reflector toward the secondary image surface in theorder of a light beam path from the image display element P6. As shownin FIG. 42, the respective optical surfaces of the projection opticalsystem are rotationally symmetric about an optical axis AXIS6. In FIG.42, a broken line indicates an unused and therefore removed part of thereflectors RR61 and RR62 of the second optical system L62.

Table 7 shows data for numeric value example 6 of applying specificnumeric values to the projection optical system according to the sixthembodiment.

TABLE 7 F number F/3.0 Inch size 50″ Glass (e-line refractive Curvatureradius Interval index/Abbe number) Display element INF 1.400 surface 1INF 27.300 1.51872/64.00 2 INF 12.000 1.83962/42.75 3 INF 8.613 4−66.70934 4.619 1.76167/27.31 5 −40.20806 1.466 6 33.43195 7.4491.76167/27.31 7 131.35118 14.577 8 59.72796 5.955 1.48914/70.24 9−30.09630 3.000 1.75456/34.77 10 18.28717 0.100 11 18.17450 7.2461.48914/70.24 12 −23.90429 1.977 13 −21.85215 3.000 1.81081/40.49 14−303.96553 0.100 15 109.80180 7.224 1.48914/70.24 16 −28.10454 0.100Diaphragm INF 99.059 17 182.80303 15.241 1.67764/31.92 18 −135.375280.100 19 64.12991 10.744 1.52033/58.69 20 119.23170 10.935 21 −280.887073.000 1.72793/37.72 22 114.79624 216.118 23 Aspheric surface −73.93950−120.000 Reflector (first mirror) 24 Aspheric surface −69.01404 229.652Reflector (second mirror) Projected image 0.000 surface Asphericcoefficient for surface 23 K −8.47354e−001 A4 −4.50856e−007 A6−5.49282e−011 A8 7.19838e−015 A10 −3.75857e−019 Aspheric coefficient forsurface 24 K −1.43979e+001 A4  3.27859e−008 A6 −1.83925e−012 A85.76078e−017 A10 −7.70233e−022

According to numeric value example 6, the image display element P6represents a liquid crystal device such as reflective dot matrix liquidcrystal and is designed to be telecentric. The image display element P6has an aspect ratio of 16:9, contains 1920×1080 pixels, and sizes to0.61 inches. The image display element P6 is enlarged to 50 inches forprojection. The F number is 3.0. The pixel size is approximately 7 μm onthe image display element P6 and approximately 0.58 mm on the screen S6.

FIG. 44 shows a spot diagram for the projection optical system accordingto numeric value example 6. FIG. 45 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element P6 shown in FIG.43. Reference wavelengths are 656.28 nm, 620.0 nm, 587.56 nm, 546.07 nm,460.0 nm, and 435.84 nm. The scale for FIG. 44 is twice as large as onepixel on the screen. As shown in FIG. 44, the sufficient image formationcapability results. As shown in FIG. 45, no remarkable image distortionis found and the sufficient capability results.

When the projection optical system according to the sixth embodiment isapplied to a projector (projection-type image display apparatus), theprojection optical system can be slimed by disposing plane mirrors atappropriate positions similarly to the above-mentioned first and fourthembodiments.

Seventh Embodiment

FIG. 46 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a seventh embodiment of the invention. FIG. 47 showsan enlarged view of the projection optical system.

In the diagram illustrating the seventh embodiment, P7 denotes an imagedisplay element. The image display element P7 forms the primary imagesurface. The image display element P7 can represent a reflectivedot-matrix liquid crystal panel, a digital micro mirror device (DMD),and the like. In the diagram, PP7 denotes a polarizing beam splitter(PBS), a dichroic prism, a TIR (Total Internal Reflector) prism, and thelike. STOP denotes a diaphragm. While the projector needs anillumination optical system to illuminate the image display element P7,the illumination optical system is omitted from FIGS. 46 and 47.

L71 denotes a first optical system composed of a refracting opticalelement. L72 denotes a second optical system composed of reflectors R71and R72. The projection optical system is composed of the first opticalsystem L71 and the second optical system L72 and guides the light(primary image surface) image-modulated by the image display element P7to the screen S7 to form an image (secondary image surface) on thescreen S7. The first optical system L71 forms an intermediate image atposition II in FIGS. 46 and 47. The image is then reflected onreflectors R71 and R72 to form a pupil image that is then formed on thescreen S7. As shown in FIG. 47, the respective optical surfaces of theprojection optical system are rotationally symmetric about an opticalaxis AXIS7. In FIG. 47, a broken line indicates an unused and thereforeremoved part of the reflectors R71 and R72 of the second optical systemL72.

Table 8 shows data for numeric value example 7 of applying specificnumeric values to the projection optical system according to the seventhembodiment.

TABLE 8 F number F/3.0 Inch size 52.5″ Curvature Glass (e-linerefractive radius Interval index/Abbe number) Display element INF 1.400surface 1 INF 20.700 2 INF 12.000 1.83962/42.8 3 INF 27.300 1.51872/64.04 INF 6.050 5 59.22241 12.300 1.49845/81.2 6 −86.13954 4.172 7 44.252139.409 1.49845/81.2 8 −96.55688 4.207 9 −50.21938 1.779 1.81184/33.0 1034.23739 3.003 11 38.84939 10.553 1.49845/81.2 12 −33.38322 2.575 13−35.32416 1.574 1.81184/33.0 14 −294.59246 8.563 15 −2771.84910 5.0431.85505/23.6 16 −49.26150 10.336 Diaphragm INF 32.667 17 −31.30247 1.8001.83962/42.8 18 −41.95428 21.541 19 45.68213 15.174 1.59142/61.0 20−179.12544 11.472 21 −84.96068 2.526 1.81263/25.3 22 −513.97498 0.300 2338.82080 7.423 1.67340/46.9 24 55.78713 11.970 25 −68.01291 8.0001.80831/46.3 26 45.75187 14.403 27 −55.92187 13.306 1.81081/40.5 28−48.48920 170.904 29 Aspheric surface 1.01174E−05 −151.155 Reflector(first mirror) 30 Aspheric surface 68.49207 364.319 Reflector (secondmirror) Projected INF image surface Aspheric coefficient for surface 29K −28531.19104 A4  0.124362E−07 A6 0.196046E−11 A8 −0.206541E−15 A100.103413E−19 A12 −0.290651E−24 A14 0.357592E−29 Aspheric coefficient forsurface 30 K −2.4470 A1 −1.1474E−02 A3 1.3489E−06 A4  1.1430E−07 A51.8548E−11 A6 −6.0609E−12 A8 2.8004E−16 A10 −6.6302E−21 A12 6.8785E−26A14  4.6396E−31

According to numeric value example 7, the 30th surface, i.e., a concavereflector R72 contains an aspheric coefficient of odd-numbered degree.Therefore, the above-mentioned equation 2 defines the shape of the 30thsurface.

According to numeric value example 7, the image display element P7 hasan aspect ratio of 16:9, contains 1920×1080 pixels, and sizes to 0.61inches. The image display element P7 is enlarged to 52.5 inches forprojection. The F number is 3.0. The pixel size is approximately 7 μm onthe image display element and approximately 0.605 mm on the screen S7.

FIG. 49 shows a spot diagram for the projection optical system accordingto numeric value example 7. FIG. 50 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element P7 shown in FIG.48. Reference wavelengths are 656.28 nm, 620.0 nm, 587.56 nm, 546.07 nm,460.0 nm, and 435.84 nm. The scale for FIG. 49 is twice as large as onepixel on the screen S7. As shown in FIG. 49, the sufficient imageformation capability results. As shown in FIG. 50, no remarkable imagedistortion is found and the sufficient capability results.

When the projection optical system according to the seventh embodimentis applied to a projector (projection-type image display apparatus), theprojection optical system can be slimed by disposing plane mirrors atappropriate positions similarly to the above-mentioned first and fourthembodiments.

Eighth Embodiment

FIG. 51 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to an eighth embodiment of the invention. FIG. 52 showsan enlarged view of the projection optical system.

In the diagram illustrating the eighth embodiment, P8 denotes an imagedisplay element. A primary image surface is formed on the image displayelement P8. The image display element P8 can represent a digital micromirror device (DMD). While the projector needs an illumination opticalsystem to illuminate the image display element P8, the illuminationoptical system is omitted from FIGS. 51 and 52.

L81 denotes a first optical system composed of a refracting opticalelement. L82 denotes a second optical system composed of reflectors RR81and RR82. The projection optical system is composed of the first opticalsystem L81 and the second optical system L82 and guides the light(primary image surface) image-modulated by the image display element P8to the screen S8 to form an image (secondary image surface) on thescreen S8. The first optical system L81 forms an intermediate image atposition II in FIGS. 51 and 52. The image is then reflected onreflectors RR81 and RR82 to form a pupil image that is then formed onthe screen S8. As shown in FIG. 52, the respective optical surfaces ofthe projection optical system are rotationally symmetric about anoptical axis AXIS8. In FIG. 52, a broken line indicates an unused andtherefore removed part of the reflectors RR81 and RR82 of the secondoptical system L82.

Table 9 shows data for numeric value example 8 of applying specificnumeric values to the projection optical system according to the eighthembodiment.

TABLE 9 F number F/3.0 Inch size 55.8″ Glass (e-line refractiveCurvature radius Interval index/Abbe number) Display element INF 54.000surface Diaphragm INF 0.100 1 71.13311578 3.000 1.76167/27.31 2−132.8219538 6.435 3 87.24914913 9.995 1.76167/27.31 4 −111.03702 0.1005 −477.69876 3.000 1.80932/39.39 6 34.30104 1.000 7 42.77973 6.8411.56605/60.58 8 −22.24372 3.000 1.73432/28.10 9 49.09361 0.100 1044.96886 5.684 1.48914/70.24 11 −52.48688 51.478 12 −931.71066 5.0001.76167/27.31 13 −302.78002 70.336 14 94.02440 7.538 1.76167/27.31 15298.10396 6.199 16 −186.511621 5.000 1.74794/44.63 17 1081.95709 285.51718 Aspheric surface −83.79108 −110.000 Reflector (first mirror) 19Aspheric surface −177.21176 260.000 Reflector (second mirror) Projectedimage INF 1.000 surface Aspheric coefficient for surface 18 K−6.03097e−001 A4  2.98655e−007 A6 −1.62107e−011 A8 1.53773e−015 A10−2.42130e−020 A12 −2.52893e−024 Aspheric coefficient for surface 19 K−2.90510e+001 A4  7.12285e−008 A6 −8.49805e−012 A8 6.28723e−016 A10−2.49940e−020 A12  3.55011e−025

According to numeric value example 8, a DMD is used as the image displayelement P8 that has an aspect ratio of 16:9, contains 1280×768 pixels,and sizes to 0.7 inches. The image display element P8 is enlarged to55.8 inches for projection. The F number is 3. The pixel size isapproximately 12 μm on the image display element P8 and approximately0.86 mm on the screen S8. A diaphragm STOP is provided between the imagedisplay element P8 and the projection optical system. ON light isreflected on the image display element P8, passes through the diaphragmSTOP and the projection optical system, and then reaches the screen S8.The diaphragm STOP interrupts OFF light. The ON light passes through thediaphragm STOP and enters the refracting optical system L81 to form anintermediate image at the position II in FIGS. 51 and 52. The ON lightis then reflected on the reflector RR81 to form a pupil image. The imageis reflected on the reflector RR82 to be formed on the screen S8.

FIG. 54 shows a spot diagram for the projection optical system accordingto numeric value example 8. FIG. 55 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element shown in FIG.53. Reference wavelengths are 656.28 nm, 620.0 nm, 587.56 nm, 546.07 nm,460.0 nm, and 435.84 nm. The scale for FIG. 54 is twice as large as onepixel on the screen S8. As shown in FIG. 54, the sufficient imageformation capability results. As shown in FIG. 55, no remarkable imagedistortion is found and the sufficient capability results.

When the projection optical system according to the eighth embodiment isapplied to a projector (projection-type image display apparatus), theprojection optical system can be slimed by disposing plane mirrors atappropriate positions similarly to the above-mentioned first throughfourth embodiments.

Ninth Embodiment

FIG. 56 outlines the entire optical system of a projector(projection-type image display apparatus) using the projection opticalsystem according to a ninth embodiment of the invention. FIG. 57 showsan enlarged view of the projection optical system.

In the diagram illustrating the ninth embodiment, P9 denotes an imagedisplay element. The image display element P9 forms the primary imagesurface. The image display element P9 can represent a reflectivedot-matrix liquid crystal panel, a digital micro mirror device (DMD),and the like. In the diagram, PP9 denotes a polarizing beam splitter(PBS), a dichroic prism, a TIR (Total Internal Reflector) prism, and thelike. STOP denotes a diaphragm. While the projector needs anillumination optical system to illuminate the image display element P9,the illumination optical system is omitted from FIGS. 56 and 57.

L91 denotes a first optical system composed of a refracting opticalelement. L92 denotes a second optical system composed of a reflectorAM9. The projection optical system is composed of the first opticalsystem L91 and the second optical system L92 and guides the light(primary image surface) image-modulated by the image display element P9to the screen S9 to form an image (secondary image surface) on thescreen S9. That is, the first optical system L91 forms an intermediateimage at position II in FIGS. 56 and 57. The image is then reflected ona reflector AM9 to form a pupil image that is then formed on the screenS9. As shown in FIG. 57, the respective optical surfaces of theprojection optical system are rotationally symmetric about an opticalaxis AXIS9. In FIG. 57, a broken line indicates an unused and thereforeremoved part of the concave reflector AM9 of the second optical systemL92.

Table 10 shows data for numeric value example 9 of applying specificnumeric values to the projection optical system according to the ninthembodiment.

TABLE 10 F number F/3.0 Inch size 62.6″ Glass (e-line refractiveCurvature radius Interval index/Abbe number) Display element INF 0.900surface 1 INF 30.000 1.51872/64.0 2 INF 5.000 3 62.65902 9.4021.48914/70.2 4 −82.6989 6.176 5 36.38095 10.475 1.49845/81.2 6 −81.1686.000 7 −37.1714 1.539 1.64940/31.7 8 27.24078 3.912 9 33.08227 10.5041.49845/81.2 10 −28.5041 2.809 11 −26.4725 1.341 1.61864/34.5 1260.76307 1.402 13 87.88232 6.476 1.75520/27.5 14 −32.7878 9.119Diaphragm INF 13.175 15 −27.9681 1.500 1.54285/47.0 16 −52.9861 18.50217 91.05025 10.217 1.75450/51.6 18 −58.8245 3.649 19 −49.6999 5.6901.84666/23.8 20 −117.323 50.536 21 68.55467 8.000 1.48914/70.2 2246.45361 14.599 23 −149.905 3.005 1.48914/70.2 24 115.63 5.973 25426.1313 6.000 1.84829/29.7 26 −670.278 250.000 27 Aspheric surface−88.935 −700.000 Reflector (first mirror) Projected image surfaceAspheric coefficient for surface 27 K −2.641049 A4 −0.111535E−06 A6 0.386529E−11 A8 −0.317841E−16 A10 −0.822479E−20 A12  0.452284E−24 A14−0.631588E−29 A16 −0.186046E−33 A18 0.528090E−38

According to numeric value example 9, the image display element P9represents a liquid crystal device such as reflective dot matrix liquidcrystal and is designed to be telecentric. The image display element P9has an aspect ratio of 16:9, contains 1920×1080 pixels, and sizes to0.61 inches. The image display element P6 is enlarged to 62.6 inches forprojection. The F number is 3.0. The pixel size is approximately 7 μm onthe image display element P9 and approximately 0.725 mm on the screen.

FIG. 59 shows a spot diagram for the projection optical system accordingto numeric value example 9. FIG. 60 shows distortion. Field angles (1)through (15) shown in the spot diagram are respectively generated frompositions (1) through (15) on the image display element P9 shown in FIG.58. Reference wavelengths are 656.28 nm, 620.0 nm, 587.56 nm, 546.07 nm,460.0 nm, and 435.84 nm. The scale for FIG. 59 is twice as large as onepixel on the screen S9. As shown in FIG. 59, the sufficient imageformation capability results. As shown in FIG. 60, no remarkable imagedistortion is found and the sufficient capability results.

When the projection optical system according to the ninth embodiment isapplied to a projector (projection-type image display apparatus), theprojection optical system can be slimed by disposing plane mirrors atappropriate positions similarly to the above-mentioned first and fourthembodiments.

Table 11 lists related data and corresponding data for conditionalequations (1), (2), and (3) according to the above-mentioned numericvalue examples 3 to 9.

TABLE 11 Numeric Numeric Numeric Numeric Numeric Numeric Numeric valuevalue value value value value value example 3 example 4 example 5example 6 example 7 example 8 example 9 Remarks Data associated withconditional equations Si1 186 183 180 155 185 230 152 Distance betweenthe first optical system and the intermediate image surface (screenbottom) Si2 106 112 100 139 103 211 99 Distance between the firstoptical system and the intermediate image surface (screen center) Si3 4250 42 124 37 179 46 Distance between the first optical system and theintermediate image surface (screen top) Ls 211.99 131.25 213.40 195.89214.10 184.81 210.00 Total lens length of the first optical system R67.521 68.816 72.722 73.940 68.492 83.791 88.935 Curvature radius of theconcave reflector K −2.69 −2.34 −2.42 −0.85 −2.45 −0.60 −2.64 Conicconstant of the concave reflector Data corresponding to conditionalequations Si1/Ls 0.88 1.39 0.84 0.79 0.86 1.24 0.72 Si/Ls < 2 Si2/Ls0.50 0.85 0.47 0.71 0.48 1.14 0.47 Si/Ls < 2 Si3/Ls 0.20 0.38 0.20 0.630.17 0.97 0.22 Si/Ls < 2 |R|/2 33.760 34.408 38.361 36.970 34.246 41.89644.468 S12 > |R|/2 S12 321.0 323.4 320.6 216.1 322.1 285.5 250.0 SR12 >|R|/2 SR12 149.0 140.0 149.0 120.0 151.2 110.0 (−)

It can be understood that the above-mentioned numeric value examples 3to 9 all satisfy conditional equations (1), (2), and (3).

FIG. 61 shows intermediate image positions for the first optical systemL41 according to the above-mentioned embodiment 4. In FIG. 61, Si1, Si2,and Si3 denote distances between the first optical system L41 andintermediate image positions corresponding to the lowest, meddle, andhighest field angles on the screen, respectively. The positionscorrespond to points (1), (7), and (13) in FIG. 22. The distances areSi1≈183 mm, Si2≈112 mm, and Si3≈50 mm. Length Ls of the first opticalsystem L41 is 131.25 mm and satisfies conditional equation (1). Any ofnumeric value examples 3 through 9 satisfy not only conditional equation(1), but also conditional equations (2) and (3) (see Table 11).

When the above-mentioned features and effects are properly used, it ispossible to appropriately correct the distortion and compactly constructthe projection optical system excellent in the image formationcapability using a small number of reflectors.

The above-mentioned embodiments have described the projection-type imagedisplay apparatus for projection on the transmissive screen. It isobvious that the projection-type image display apparatus according tothe invention is applicable as an apparatus for projection on areflective screen.

The above-mentioned embodiments have described the first optical systemand the second optical system composed of the surfaces that arerotationally symmetric about the common optical axis. In addition, theinvention is also applicable to surfaces that are not rotationallysymmetric.

The above-mentioned embodiments and numeric value examples haverepresented the specific shapes and numeric values for the components asmere examples of embodying the invention. These specifics must not causethe technical scope of the invention to be interpreted restrictively.

INDUSTRIAL APPLICABILITY

The invention can provide the projection optical system that features asmall depth and height and a large enlargement factor. The projectionoptical system is particularly appropriately applied to a large rearprojection television. In addition, the projection optical system isappropriate for enlarged projection onto a reflective screen and thelike in a limited space such as a narrow room.

1. A projection optical system for enlarged projection from a primaryimage surface existing at a reducing side to a secondary image surfaceexisting at an enlarging side, comprising: a first optical system thatforms an intermediate image of the primary image surface; and a secondoptical system having a concave reflector that forms the secondary imagesurface according to the intermediate image, wherein a light beamtravels from the center of the primary image surface to the center ofthe secondary image surface, crosses an optical axis of the firstoptical system, reflects on the concave reflector, crosses the opticalaxis again, and reaches the secondary image surface.
 2. The projectionoptical system according to claim 1, wherein the first optical systemand the second optical system include surfaces that are rotationallysymmetric about a common optical axis.
 3. The projection optical systemaccording to claim 2, wherein the second optical system comprises onlythe concave reflector.
 4. The projection optical system according toclaim 2, wherein the second optical system has a convex reflector towardan enlarging side or reducing side of the concave reflector.
 5. Theprojection optical system according to claim 2, wherein the firstoptical system forms the intermediate image toward the primary imagesurface rather than the concave reflector of the second optical system.6. The projection optical system according to claim 5, whereinconditional equation (1) below is satisfied where Ls is a length alongthe optical axis between a light entrance surface and a light existsurface of the first optical system and Si is a distance along theoptical axis between the light entrance surface of the first opticalsystem and the intermediate image.Si/Ls<2  (1)
 7. The projection optical system according to claim 5,wherein conditional equation (2) below is satisfied where S12 is adistance between the first optical system and the concave reflector andR is a paraxial curvature radius of the concave reflector.S12>|R|/2  (2)
 8. The projection optical system according to claim 4,wherein conditional equation (3) below is satisfied where SR12 is adistance along the optical axis between the convex reflector and theconcave reflector.SR12>|R|/2  (3)
 9. The projection optical system according to claim 2,wherein the concave reflector is a rotationally symmetric and asphericsurface about the optical axis.
 10. The projection optical systemaccording to claim 9, wherein a function indicating a shape of therotationally symmetric and aspheric surface contains an asphericcoefficient of odd-numbered degree.
 11. The projection optical systemaccording to claim 9, wherein the concave reflector is shaped todecrease a curvature against a paraxial curved surface as the concavereflector becomes distant from the optical axis.
 12. The projectionoptical system according to claim 4, wherein the convex reflectorcontains at least one rotationally symmetric and aspheric surface. 13.The projection optical system according any of to claims 2 through 5,wherein the first optical system contains one or more rotationallysymmetric and aspheric surfaces. 14-20. (canceled)